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352

BREAST BONE

vertebra, though hardly at all marked, is nevertheless really
present and developed from a bony centre of its own, as in other
mammals. The dorsal and lumbar vertebrae are, of course, to be
distinguished by the presence of ribs attached to the former; but

FIG. 186.—Section through middle
line of united cervical vertebrae
of Greenland Bight Whale (Jlal-
aena mysticelus}. x -J-. a, Arti-
cular surface for occipital coxidyle;
e, epiphysis on posterior end of
body of seventh cervical vertebra ;
sn, foramen in arch of atlas for
first spinal nerve ; 1, arch of atlas ;
2, 3, 4, 5, 6, conjoined arches of
the axis and four following verte-
brae ; 7, arch of seventh vertebra.
(From Flower's Osteology.}

as there is only a rudimentary pelvis, not attached to the
vertebral column, no sacral region can be detected. The caudal
vertebrae are to be recognised by the V-shaped chevron bones
below.

FlO. 187.—A, Sternum of Greenland Right Whale (Balaena mysticetus). x •&. B,
Sternum of Common Rorqual or Fin Whale (Halaenoptera muscitlus). x A.
(From Flower's Osteology.)
The sternum in the Whale tribe is much more modified in the
Whalebone Whales than in the Odontocetes. In the latter it is
made up of several pieces, as its. other mammals, which often,
however, become coalesced. In the Mystacoceti this bone is a
piece, to which only one pair of ribs is attached, and its